Front end circuit and wireless communication device

Abstract

A front end circuit includes a variable matching circuit connected to a diplexer and a switch connector connected between an antenna port and the diplexer. The variable matching circuit selectively connects matching circuits to a signal path. When one of the matching circuits is connected, the impedance as viewed from the switch connector matches an impedance of a measurement circuit near a normalized impedance of 1 in a predetermined communication band, whereas when the other matching circuit is connected, the impedance viewed from the antenna port conjugate-matches the impedance of an antenna circuit in a predetermined communication band.

The invention claimed is: 
     
       1. A front end circuit having a transmission port into which a transmission signal in a first predetermined communication band is inputted, a reception port from which a reception signal in a second predetermined communication band is outputted, and an antenna port from which the transmission signal is outputted and the reception signal is inputted, the front end circuit comprising:
 a shared antenna device connected between the antenna port, and the transmission port and the reception port; 
 a variable matching circuit connected to the shared antenna device; and 
 a measurement terminal connecting unit connected between the antenna port and the shared antenna device or between the antenna port and the variable matching circuit, 
 wherein the variable matching circuit includes: 
 a first matching circuit for matching near a normalized impedance of 1 and a second matching circuit for conjugate matching, the first matching circuit and the second matching circuit having mutually different impedances; and 
 a connection selection unit that connects the first matching circuit or the second matching circuit to the shared antenna device. 
 
     
     
       2. The front end circuit according to  claim 1 ,
 comprising a plurality of the second matching circuits, wherein each of the plurality of second matching circuits has a different impedance. 
 
     
     
       3. The front end circuit according to  claim 1 ,
 wherein the second matching circuit is a variable impedance circuit. 
 
     
     
       4. The front end circuit according to  claim 1 , further comprising:
 a transmission filter connected to the transmission port and a reception filter connected to the reception port. 
 
     
     
       5. The front end circuit according to  claim 4 , further comprising:
 a circulator connected between the transmission filter and the reception filter. 
 
     
     
       6. The front end circuit according to  claim 4 ,
 wherein the transmission filter and the reception filter are each constituted of a tunable filter having a variable reactance element or a selectable filter having a switch and a plurality of filters. 
 
     
     
       7. The front end circuit according to  claim 1 ,
 wherein the shared antenna device is a diplexer that separates transmission signals and reception signals in a low-frequency communication band and transmission signals and reception signals in a high-frequency communication band. 
 
     
     
       8. A wireless communication device comprising:
 the front end circuit according to  claim 1 ; and 
 an antenna circuit that includes an antenna and is connected to the front end circuit through the antenna port. 
 
     
     
       9. A wireless communication device including a front end circuit, the front end circuit having a transmission port into which a transmission signal in a predetermined communication band is inputted, a reception port from which a reception signal in a predetermined communication band is outputted, and an antenna port from which the transmission signal is outputted and the reception signal is inputted, the wireless communication device comprising:
 an antenna circuit that includes an antenna and is connected to the front end circuit through the antenna port; 
 a shared antenna device connected between the antenna port, and the transmission port and the reception port in the front end circuit; 
 a variable matching circuit connected to the shared antenna device in the front end circuit; and 
 a measurement terminal connecting unit provided in the antenna circuit, 
 wherein the variable matching circuit includes: 
 a first matching circuit for matching near a normalized impedance of 1 and a second matching circuit for conjugate matching, the first matching circuit and the second matching circuit having mutually different impedances; and 
 a connection selection unit that connects the first matching circuit or the second matching circuit to the shared antenna device. 
 
     
     
       10. The wireless communication device according to  claim 9 , comprising:
 a proximity sensor that detects a proximity state of an object to the antenna; and 
 a control unit that controls the connection selection unit to connect the second matching circuit to the shared antenna device when the proximity sensor has detected a proximity state in which an object is near the antenna. 
 
     
     
       11. The wireless communication device according to  claim 9 , comprising:
 a proximity sensor that detects a proximity state of an object to the antenna; and 
 a control unit that controls the connection selection unit to connect the second matching circuit to the shared antenna device when the proximity sensor has detected a proximity state in which an object is near the antenna. 
 
     
     
       12. The wireless communication device according to  claim 9 , comprising:
 an impedance matching detection circuit provided in the antenna circuit or the front end circuit; and 
 a control unit that controls the connection selection unit to connect the second matching circuit to the shared antenna device when the impedance matching detection circuit has detected an impedance mismatch. 
 
     
     
       13. The wireless communication device according to  claim 9 , comprising:
 an impedance matching detection circuit provided in the antenna circuit or the front end circuit; and 
 a control unit that controls the connection selection unit to connect the second matching circuit to the shared antenna device when the impedance matching detection circuit has detected an impedance mismatch. 
 
     
     
       14. The wireless communication device according to  claim 10 ,
 wherein the antenna circuit further includes an antenna tuner connected between the antenna and the measurement terminal connecting unit; and 
 the antenna tuner is a variable impedance circuit and is controlled by the control unit. 
 
     
     
       15. The wireless communication device according to  claim 11 ,
 wherein the antenna circuit further includes an antenna tuner connected between the antenna and the measurement terminal connecting unit; and 
 the antenna tuner is a variable impedance circuit and is controlled by the control unit. 
 
     
     
       16. The wireless communication device according to  claim 12 ,
 wherein the antenna circuit further includes an antenna tuner connected between the antenna and the measurement terminal connecting unit; and 
 the antenna tuner is a variable impedance circuit and is controlled by the control unit. 
 
     
     
       17. The wireless communication device according to  claim 13 ,
 wherein the antenna circuit further includes an antenna tuner connected between the antenna and the measurement terminal connecting unit; and 
 the antenna tuner is a variable impedance circuit and is controlled by the control unit.